When and Should i wait for her to call?

Here's the story: One of my friend's female buddies have been hanging with us for several months now, and i've been spending alot of time flirting with her (mutually). Anyways, the other day I visited her while she was at work, and it got really busy so I handed her my phone number to grab lunch later, and she seemed really excited. That was four days ago. Is she making me wait? (I was under the assumption that this kind of stuff ends after high school?!?!) Does anyone have a similar experience like this? When is she going to call? Should i visit her at work again, or will that come off desperate?